Hein (fub) wrote,
Hein
fub

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Etch, etch baby!

You know how you can feel intimidated by something, and when you finally take the plunge, it's in fact no trouble at all?

Etching PCBs turned out to be just like that for us. Readers with a good memory will remember that somewhere in October last year, I bought an etch tank and exposure unit. Until now, I haven't used either of those.
With my design checked by an expert and all the tools and ingredients available, it was time to take the plunge and start to work with fluids that eat away metal -- in other words, to etch my own layout!

I printed the layout on an overhead transparency on our new laser printer, and smeared black ink all over it. Then when the ink had dried up, I used a wet piece of kitchen paper to clean off the ink from the foil -- but it stuck where the toner had been. This ensured a perfectly black layout.


We cut a standard photosensitive eurocard board in two (one for the upper side of the nixie clock, one for the driver circuit), peeled off the plastic layer that protected the photosensitive layer and positioned the sheets on top. Four minutes of exposure to UV-A softens the photosensitive layer -- so the layer under the black parts of the layout stay solid.


You then 'develop' this PCB in a caustic solution. We got two liters of 'official' developer from the guy who sold us his etching tank as a bonus, but home-etchers on a budget also use the cheap stuff to clean up blockages in the sewage system.
During this step, you can see your layout start to form: the softened photosensitive layer comes off the plate -- you can see the dark 'clouds' of dissolved stuff float around in the developer.


The result after developing. Yes, that's a plastic clothes pin I use as a pincet -- it works.


Clean off the develop-solution under the bathroom sink...


And repeat the process for the second print.


Clean exposed copper in between the traces where the photosensitive layer was protected by the layout when it was exposed to UV-A.


The etching tank, mounted in an ammunition case. The pump on the left side pumps air through the etchant, which keeps it moving. On the right, a heating element -- the etchant should be around 40 to 45 degrees Celcius.


Mount the plates in the special holder, and hang them in the etchant. Almost immediately, the copper turns a bright pinkish color where it is not protected.


We actually made two sets of PCBs, and added the second set on top of the first set about halfway the etching process. The first set (below) has been fully etched, the second set has still a ways to go.


Dipping the PCBs into the etchant to get rid of the last copper traces that were under the holder.


All done! A shiny new PCB, to your own specifications!
All you have to do now is to remove the photosensitive layer with a bit of aceton (nailpolish remover) to get to the clean copper.


Next, take your dremel clone, mount a PCB drill, and start drilling!

My only regret is that I did not put a bit of text or a picture in the big copper squares I put in the layout. There are no components there, and it's a bit of a waste of etchant to etch copper that doesn't interfere with anything. I should have put my user icon in there, or something to 'brand' the PCB. Next time!
Tags: electronics project
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